As fighting in Sri Lanka intensified, Channel 4 News obtained exclusive satellite photos showing the dramatic movement of refugees as they fled repeated bombardment.

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This report by Asia correspondent Nick Paton Walsh contains images that some viewers may find disturbing.

Journalists were not allowed into the area where Tamil Tiger refugee camps were set up, but exclusive satellite images obtained by Channel 4 News showed the changes in migration.

Channel 4 News asked experts to analyse satellite images taken of the 3km square zone early on Sunday 10 May 2009.

In one image, the area outlined in red was where around 11,300 tents stood just a week before the images were taken. The yellow areas show where the tents have moved to.

Sri Lanka satellite images

Channel 4 News asked experts to analyse satellite images taken of the 3km square zone.

Two close-ups show the scale of this migration away from one small area.

The image on the left shows the number of tents in the area before the weekend, and the image on the right is the same area after the weekend.

It is not possible to say if the shelling happened before or after the people fled, but many of them moved very fast at a time when heavy shelling was reported in the area.

Sri Lanka satellite images
Nick Paton Walsh blog: mystery deepens
If you look at a satellite image of the area, you can see dozens of craters - the pock marks that one analyst said were consistent with "widespread shelling". These are areas where, two weeks ago, there were dozens of tents instead.
The mystery of where all the people have gone deepens. Satellite pictures from a week ago show 11,300 tents, one analysis suggests. Aid workers think about eight people lived in each tent - that's a guess, but one based on the density of people there about a month ago.
After the weekend, a fresher image shows the tents have completely moved. There are now fewer of them, it seems, cramped into tiny pockets on the southern flank of the area.
One aid worker told me they think each tent might account for 16 people. Where the tents used to be, to the north, there are dozens of craters. It's impossible to know if they were made before the tents moved, or after.

Read more from Nick Paton Walsh's blog

This image shows two craters that could be seen on Sunday but were not there the previous Wednesday. The analysts says they are consistent with "widespread shelling".

Satellite images of Sri Lanka

The army has said there was no shelling happening at all; then it said Tamil Tigers are shelling themselves. But 430 people were killed in just two days.

The day Nick Paton Walsh's report was aired pictures emerged of an attack on the no-fire zone.

We cannot verify the authenticity of the images, but doctors say shelling hit the make-shift hospital leaving 45 dead including their own colleagues.

The Sri Lankan government again said it was not shelling the area. Sri Lankan Defence Spokesman, Minister Keheliya Rambukwelle called it "a total fabrication" and " a blatant lie". He said the Sri Lankan authorities "totally and categorically deny" the reports.

Sexual abuse in refugee camps
Channel 4 News
's report on sexual abuse and disappearances from the Tamil refugee camp in the Sri Lankan city of Vavuniya led to Asia correspondent Nick Paton Walsh being expelled from the country.

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